Light emitting device (LED) and multi-stacked LED including charge generation junction (CGJ) layer, and manufacturing method thereof

ABSTRACT

Provided is a light emitting diode (LED) and a multi-stacked LED including a charge generation junction (CGJ) layer, and a manufacturing method thereof. An LED including an anode, a hole transport layer, a light emitting layer, and a cathode, includes a CGJ layer in a layer-by-layer structure in which an n-type oxide and a p-type oxide formed on at least one surface of the light emitting layer are sequentially stacked. Here, the n-type oxide includes zinc oxide (ZnO) and the p-type oxide is represented by the following Formula: Cu2Sn2-XS3—(GaX)2O3. Here, 0.2&lt;x&lt;1.5.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2019-0085362 filed on Jul. 15, 2019, which is herebyincorporated by reference in its entirety.

BACKGROUND 1. Field

The following description of embodiments relates to a light emittingdevice (LED) and a multi-stacked LED including a charge generationjunction (CGJ) layer, and a manufacturing method thereof.

2. Related Art

Currently, a quantum dot emitting diode (QLED) is in the spotlight dueto excellent properties, such as, for example, variable color emission,wide color gamut, and low manufacturing cost.

Since the QLED was first release in 1994, device performance has beencontinuously improved with the development of high quality quantum dot(QD) materials and device architectures.

Further, the current efficiency (CE) and external quantum efficiency(EQE) of the QLED are similar to those of a state-of-the-art organiclight emitting diode (OLED) and accordingly, the QLED is expected to becommercialized as one of next-generation displays.

However, despite the great improvement in the device efficiency, theoperation life of the QLED is much less than that of a commercial OLED.

A series structure that connects two or three electroluminescent (EL)devices in series using a charge generation junction (CGJ) provides highCE and long operation life, and is widely used for an OLED display andlighting.

According to the related art, CGJ formed through a solution processincludes a p-type semi-continuous polymer, such as a conductive polymerPEDOT:PSS, and an n-type metal oxide, such as zinc oxide (ZnO) and ZnOdoped with lithium (Li).

However, acidic properties of PEDOT:PSS cause damage to the surface ofindium tin oxide (ITO) and degrade CGJ properties and device performancein reaction to ZnO.

It is well known that inorganic p-type materials, such as Cu₂O, NiOx,Cu:NiOx, WOx, and CuSCN, may be used as a hole injection layer of QLEDinstead of using a hole injection layer that includes PEDOT:PSS.

However, most hole injection layers including metal oxides generallyrequire a long-hour and high-temperature annealing process to acquirethe adequate transparency and conductivity and some p-type metal oxidesrequire subsequent UV-ozone treatment.

Such high-temperature annealing and ultraviolet (UV)/O₃ treatment maydegrade a quantum dot function of the QLED.

REFERENCES

-   Patent document 1: Korean Patent Registration No. 10-1812896,    “quantum dot light emitting device including solution processed    charge generation junction and manufacturing method thereof”-   Patent document 2: Korean Patent Registration No. 10-1772437, “light    emitting device fabricated utilizing charge generation layer formed    by solution process and fabrication method thereof”

SUMMARY

An embodiment provides a light emitting diode (LED) having an excellentcapability of generating and transporting charge by including a chargegeneration junction (CGJ) layer formed using an n-type oxide and ap-type oxide different from conventional PEDOT:PSS.

An embodiment also provides an LED having the excellent currentefficiency (CE) and external quantum efficiency (EQE) by forming a CGJlayer having an excellent capability of generating and transportingcharge.

An embodiment also provides a multi-stacked LED having an improvedcapability of generating and transporting charge and improved electricalproperties by forming a CGJ layer between light emitting layers in themulti-stacked LED including at least two light emitting layers.

An embodiment also provides a method of manufacturing an LED that mayperform a manufacture on a large scale by forming a CGJ layer through asolution process and by reducing a process time and may prevent damageto a device by proceeding at a low temperature.

According to an aspect, there is provided an LED including an anode, ahole transport layer, a light emitting layer, and a cathode, the LEDincluding a charge generation junction (CGJ) layer in a layer-by-layerstructure in which an n-type oxide and a p-type oxide formed on at leastone surface of the light emitting layer are sequentially stacked. Here,the n-type oxide includes zinc oxide (ZnO), and the p-type oxide isrepresented by the following formula:Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula]

Here, 0.2<x<1.5.

The n-type oxide and the p-type oxide may have the band gap energy of3.0 eV or more.

The n-type oxide may be ZnO doped with a dopant.

The dopant may include at least one of cesium (Cs), lithium (Li),aluminum (Al), magnesium (Mg), indium (In), and gallium (Ga).

The light emitting layer may include at least one of a quantum dot, anoxide layer, a nitride layer, a semiconductor layer, an organic compoundlayer, an inorganic compound layer, a phosphor layer, and a dye layer.

The LED may have the current efficiency (CE) of 1 cd/A to 100 cd/A.

The LED may have the external quantum efficiency (EQE) of 5% to 25%.

According to an aspect, there is provided a multi-stacked LED includingan anode, a hole transport layer, at least two light emitting layers,and a cathode, the multi-stacked LED including a CGJ layer in which alayer-by-layer structure in which an n-type oxide and a p-type oxide aresequentially stacked is formed between the at least two light emittinglayers. Here, the n-type oxide includes zinc oxide (ZnO), and the p-typeoxide is represented by the following formula:Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula]

Here, 0.2<x<1.5.

The n-type oxide and the p-type oxide may have the band gap energy of3.0 eV or more.

The n-type oxide may be ZnO doped with a dopant.

The dopant may include at least one of cesium (Cs), lithium (Li),aluminum (Al), magnesium (Mg), indium (In), and gallium (Ga).

The multi-stacked LED may have the current efficiency (CE) of 3 cd/A to300 cd/A.

The multi-stacked LED may have the external quantum efficiency (EQE) of15% to 75%.

According to an aspect, there is provided a method of manufacturing anLED, the method including forming an anode on a substrate; forming ahole transport layer on the anode; forming a light emitting layer on thehole transport layer; forming a cathode on the light emitting layer; andforming a CGJ layer on at least one surface of the light emitting layer.Here, the CGJ layer is formed through film formation with a solutionthat includes an n-type oxide including zinc oxide (ZnO) and a p-typeoxide represented by the following formula:Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula]

Here, 0.2<x<1.5.

The CGJ layer may be applied with heat treatment or ultraviolet(UV)/ozone treatment.

The heat treatment may be performed at 150° C. to 250° C.

The heat treatment may be performed for 10 minutes to 90 minutes.

The UV/ozone treatment may be performed for 30 seconds to 5 minutes.

According to some embodiments, it is possible to provide an LED havingan excellent capability of generating and transporting charge byincluding a CGJ layer formed using an n-type oxide and a p-type oxidedifferent from conventional PEDOT:PSS.

According to some embodiments, it is possible to provide an LED havingthe excellent current efficiency (CE) and external quantum efficiency(EQE) by forming a CGJ layer having an excellent capability ofgenerating and transporting charge.

According to some embodiments, it is possible to provide a multi-stackedLED having an improved capability of generating and transporting chargeand improved electrical properties by forming a CGJ layer between lightemitting layers in a multi-stacked LED including at least two lightemitting layers.

According to some embodiments, it is possible to provide a method ofmanufacturing an LED that may perform a manufacture on a large scale byforming a CGJ layer through a solution process and by reducing a processtime and may prevent damage to a device by proceeding at a lowtemperature.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments will be described in more detail with regard to the figures,wherein like reference numerals refer to like parts throughout thevarious figures unless otherwise specified, and wherein:

FIG. 1A is a cross-sectional view illustrating a detailed structure of aconventional light emitting device (LED), and FIGS. 1B to 1D arecross-sectional views illustrating an overall structure of an LEDaccording to an embodiment.

FIG. 2A illustrates a current flow of a charge generation junction (CGJ)layer in forward bias of an LED according to an embodiment, and FIG. 2Billustrates a current flow of a CGJ layer in reverse bias of an LEDaccording to an embodiment.

FIG. 3 is a graph showing current-voltage properties of a CGJ layer inforward bias and reverse bias of an LED according to an embodiment.

FIGS. 4A and 4B are cross-sectional views illustrating a detailedstructure of a multi-stacked LED according to an embodiment.

FIG. 5 is a flowchart illustrating a process of manufacturing an LEDaccording to an embodiment.

FIG. 6 illustrates a process of manufacturing a CGJ layer according toan embodiment.

FIG. 7 is a graph showing optical band gap properties of an n-type oxideand a p-type oxide of an LED according to an embodiment.

FIG. 8 is a graph showing transmittance of a CGJ layer according to anembodiment.

FIG. 9A is a graph showing a current-voltage curve of an LED accordingto an embodiment, FIG. 9B is a graph showing a luminance-voltage curveof an LED according to an embodiment, FIG. 9C is a graph showing acurrent efficiency-luminance curve according to an embodiment, and FIG.9D is a graph showing a power efficiency-luminance curve according to anembodiment.

FIG. 10A is a graph showing a current-voltage curve of a blue LED and amulti-stacked blue LED according to an embodiment, FIG. 10B is a graphshowing a luminance-voltage curve of a blue LED and a multi-stacked blueLED according to an embodiment, FIG. 10C is a graph showing a currentefficiency-luminance curve of a blue LED and a multi-stacked blue LEDaccording to an embodiment, and FIG. 10D is a graph showing an externalquantum efficiency-luminance curve of a blue LED and a multi-stackedblue LED according to an embodiment.

FIG. 11A is a graph showing a current-voltage curve of a green LED and amulti-stacked green LED according to an embodiment, FIG. 11B is a graphshowing a luminance-voltage curve of a green LED and a multi-stackedgreen LED according to an embodiment, FIG. 11C is a graph showing acurrent efficiency-luminance curve of a green LED and a multi-stackedgreen LED according to an embodiment, and FIG. 11D is a graph showing anexternal quantum efficiency-luminance curve of a green LED and amulti-stacked green LED according to an embodiment.

FIG. 12A is a graph showing a current-voltage curve of a red LED and amulti-stacked red LED according to an embodiment, FIG. 12B is a graphshowing a luminance-voltage curve of a red LED and a multi-stacked redLED according to an embodiment, FIG. 12C is a graph showing a currentefficiency-luminance curve of a red LED and a multi-stacked red LEDaccording to an embodiment, and FIG. 12D is a graph showing an externalquantum efficiency-luminance curve of a red LED and a multi-stacked redLED according to an embodiment.

FIG. 13A is a graph showing a current-voltage curve of a multi-stackedwhite LED according to an embodiment, FIG. 13B is a graph showing aluminance-voltage curve of a multi-stacked white LED according to anembodiment, FIG. 13C is a graph showing a current efficiency-luminancecurve of a multi-stacked white LED according to an embodiment, and FIG.13D is a graph showing an external quantum efficiency-luminance curve ofa multi-stacked white LED according to an embodiment.

FIG. 14A is an image illustrating emission of a multi-stacked white LEDaccording to an embodiment, and FIG. 14B is a graph showing an emissionspectrum of a multi-stacked white LED according to an embodiment.

FIGS. 15A and 15B are cross-sectional views illustrating an LED (e.g.,organic LED (OLED)) based on presence or absence of a CGJ layeraccording to a comparative example and an embodiment, and FIGS. 15C and15D are cross-sectional views illustrating an inverted LED (e.g., OLED)based on presence or absence of a CGJ layer according to a comparativeexample and an embodiment.

FIG. 16 is a graph showing current efficiency-luminance-power efficiencyproperties of an LED according to a comparative example and anembodiment.

FIG. 17 is a graph showing current efficiency-luminance-power efficiencyproperties of an inverted LED according to a comparative example and anembodiment.

DETAILED DESCRIPTION

The following structural or functional descriptions of embodimentsdescribed herein are merely intended for the purpose of describing theembodiments described herein and may be implemented in various forms.Here, the examples are not construed as limited to the disclosure andshould be understood to include all changes, equivalents, andreplacements within the idea and the technical scope of the disclosure.

Various modifications and changes may be made to the present disclosureand the disclosure may include various embodiments. Specific embodimentsare described in detail with reference to the accompanying drawings. Theembodiments, however, may be embodied in various different forms, andshould not be construed as being limited to only the specificembodiments. Rather, the embodiments should be understood to include allof the modifications, equivalents, and substitutions included in thespirit and technical scope of the disclosure.

Although the terms “first,” “second,” etc., may be used herein todescribe various components, the components should not be limited bythese terms. These terms are only used to distinguish one component fromanother component. For example, a first component may also be termed asecond component and, likewise, a second component may be termed a firstcomponent, without departing from the scope of this disclosure.

Hereinafter, embodiments are described with reference to theaccompanying drawings, however, the present disclosure is not limitedthereto or restricted thereby.

The terms used herein are used to simply explain specific embodimentsand are not construed to limit the present disclosure. The singularforms “a,” “an,” and “the,” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises/comprising” and “has/having” whenused in this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groups,thereof.

Also, the terms “embodiment,” “example,” “aspect,” etc., should not beinterpreted that any described aspect or design is excellent oradvantageous than other aspects or designs.

Also, the term “or” refers to “inclusive or” rather than “exclusive or.”That is, unless indicated otherwise, or unless the context clearlyindicates otherwise, the representation “x uses a or b” represents oneof natural inclusive permutations.

Also, the singular forms “a,” “an,” and “the” used in the presentspecification and claims, should be interpreted to generally indicate“at least one,” unless the context clearly indicates otherwise.

Although the terms used in the following description are selected fromgeneral and common ones in the related art, there may be other termsbased on technical development and/or change, custom, preference ofthose skilled in the art, and the like. Therefore, the terms used in thefollowing description are not construed to limit the technical spiritand should be understood as exemplary terms to explain the embodiments.

Also, in a specific case, some terms may be arbitrarily selected by theapplicant. In this case, the meaning thereof will be described in detailin the corresponding detailed description. Accordingly, the terms usedin the following description should be understood based on the meaningof the term and the overall content of the specification, not merely aname of the term.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by thoseskilled in the art to which the present disclosure pertains. Terms, suchas those defined in commonly used dictionaries, should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthe relevant art and/or this disclosure, and should not be interpretedin an idealized or overly formal sense unless expressly so definedherein.

When it is determined that detailed description related to a knownfunction or configuration may make the embodiments ambiguous indescribing the embodiments, the detailed description may be omitted.Also, the terms used herein are used to appropriately express theembodiments and may vary based on the intent of an operator or custom ofthe field to which the disclosure pertains. Accordingly, the definitionof the terms may be made based on the overall description of the presentspecification.

A light emitting device (LED) according to an embodiment includes acharge generation junction (CGJ) that includes an n-type oxide and ap-type oxide. The CGJ layer may generate a hole and an electron and mayalso transport a hole and an electron and thus, may achieve high currentefficiency and external quantum efficiency.

Herein, the term “LED” refers to an LED equipped with a singleelectroluminescent (EL) unit that includes a light emitting layer and ahole transport layer and the term “multi-stacked LED” refers to an LEDthat includes at least two EL units.

Hereinafter, a structure and a principle of an LED according to anembodiment is described with reference to the accompanying drawings.

FIG. 1A is a cross-sectional view illustrating a detailed structure of aconventional light emitting device (LED), and FIGS. 1B to 1D arecross-sectional views illustrating an overall structure of an LEDaccording to an embodiment.

Referring to FIGS. 1A to 1D, a conventional LED 100 includes a substrate(not shown), an anode 110, a hole injection layer, a hole transportlayer 131, a light emitting layer 132, an electron transport layer, anda cathode 140, and an LED 100 according to an example embodimentincludes a substrate, an anode 110, a hole transport layer 131, a lightemitting layer 132, and a cathode 140, and here, may include a chargegeneration junction (CGJ) layer 120 in a layer-by-layer structure inwhich an n-type oxide 121 and a p-type oxide 122 are sequentiallystacked on at least one surface of a light emitting layer 132.

In detail, referring to FIGS. 1B to 1D, the CGJ layer 120 according toan embodiment may be formed between the light emitting layer 132 and thecathode 140 or between the light emitting layer 132 and the anode 110,and may also be formed on both surfaces of the light emitting layer 132depending on embodiments.

The substrate refers to a base substrate for forming the LED 100. Amaterial of the substrate used in this field is not particularlylimited. For example, various materials, such as silicone, glass,plastic, and metal foil, may be used.

For example, a plastic substrate may include polyethylene terephthalate(PET), polyethylenenaphthelate (PEN), polypropylene (PP), polycarbonate(PC), polyimide (PI), tri acetyl cellulose (TAC) and polyethersulfone(PES), and a flexible substrate including one of aluminum foil andstainless-steel foil may be used.

The anode 110 is formed on the substrate (not shown) and refers to anelectrode that provides electrons to the LED 100 according to an exampleembodiment.

Depending on embodiments, the anode 110 may be formed through a solutionprocess, such as screen printing, using a transmissive electrode, areflective electrode, metal paste, or a metal ink material that is in acolloid state in a predetermined liquid.

A material for the transmissive electrode may include at least one ofindium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO₂), zincoxide (ZnO), metal oxide/metal/metal oxide multilayer, graphene, andcarbon nanotube, which are transparent and highly conductive.

A material for the reflective electrode may include at least one ofmagnesium (Mg), aluminum (Al), silver (Ag), Ag/ITO, Ag/IZO,aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), andmagnesium-silver (Mg—Ag).

The metal paste may be one of silver (Ag) paste, aluminum (Al) paste,gold (Au) paste, and copper (Cu) paste materials, or alloy thereof.

The metal ink material may include at least one of silver (Ag) ink,silver (Ag) ink, aluminum (Al) ink, gold (Au) ink, calcium (Ca) ink,magnesium (Mg) ink, lithium (Li) ink, and cesium (Cs) ink, and a metalmaterial contained in the metal ink material may be in an ionized statein a solution.

An EL unit 130 including the hole transport layer 131 and the lightemitting layer 132 may be formed on the anode 110 according to anembodiment.

The hole transport layer 131 refers to a layer configured to transportholes to the light emitting layer 132, and may be formed through a holedeposition process or a solution process using an organic material or aninorganic material.

The hole transport layer 131 may effectively transport holes to thelight emitting layer 132, and density of holes and electrons may bebalanced in the light emitting layer 132, which may lead to improvingthe luminous efficiency of the LED 100.

Also, electrons injected from the cathode 140 to the light emittinglayer 132 are trapped in the light emitting layer 132 due to an energybarrier present in an interface between the hole transport layer 131 andthe light emitting layer 132 and accordingly, a rebinding probability ofelectrons and holes increases, which may lead to improving the luminousefficiency of the LED 100.

Further, the hole transport layer 131 is formed between the lightemitting layer 132 and the CGJ layer 120, which further improves theeffect of the CGJ layer 120.

The hole transport layer 131 may be formed using, for example,PEDOT:PSS, may be formed by mixing additives, such as tungsten oxide(WO₃), graphene oxide (GO), carbon nanotube (CNT), molybdenum oxide(MoOx), vanadium oxide (V₂O₅), and nickel oxide (NiOx), to PEDOT:PSS,may be formed using an organic material such as PVK(poly(9-vinylcarbazole)), or without being limited thereto, may beformed using various organic materials or inorganic materials.

In the light emitting layer 132, holes injected from the anode 110 andelectrons injected from the cathode 140 meet and form exciton and theexciton may cause light with a specific wavelength to be generated.

The light emitting layer 132 may include one of a quantum dot, an oxidelayer, a nitride layer, a semiconductor layer, an organic compoundlayer, an inorganic compound layer, a phosphor layer, and a dye layer.

Desirably, the light emitting layer 132 may be the quantum dot lightemitting layer 132 that includes a quantum dot or may be the organiclight emitting layer 132 that includes an organic compound.

If the light emitting layer 132 is the quantum dot light emitting layer132, the quantum dot light emitting layer 132 may use at least onesemiconductor material selected from a group including group II-VIsemiconductor compounds, group III-V semiconductor compounds, groupIV-VI semiconductor compounds, group IV elements or compounds, andcombinations thereof.

The group II-VI semiconductor compounds may use at least one materialselected from a group including binary compounds selected from a groupincluding CdSe, CdS, ZnS, CdTe, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, andmixtures thereof, ternary compounds selected from a group includingCdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS,CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, andmixtures thereof, and quaternary compounds selected from a groupincluding CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe,HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof.

The group III-V semiconductor compounds may use at least one materialselected from a group including binary compounds selected from a groupincluding GaN, GaP, GaAs, GaSb, AlP, AlAs, AlSb, InN, InP, InAs, InSb,and mixtures thereof, ternary compounds selected from a group includingGaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb,InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and mixtures thereof, andquaternary compounds selected from a group including GaAlNAs, GaAlNSb,GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP,InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof.

The group IV-VI semiconductor compounds may use at least one materialselected from a group including binary compounds selected from a groupincluding SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof,ternary compounds selected from a group including SnSeS, SnSeTe, SnSTe,PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof,quaternary compounds selected from a group including SnPbSSe, SnPbSeTe,SnPbSTe, and mixtures thereof.

The group IV elements or compounds may use at least one materialselected from a group including element compounds selected from a groupincluding Si, Ge, and mixtures thereof and binary compounds selectedfrom a group including SiC, SiGe, and mixtures thereof.

Depending on embodiments, the quantum dot light emitting layer 132 mayuse, desirably, CdSe/CdS/ZnS.

The cathode 140 refers to an electrode configured to provide electronsto the LED 100 according to an embodiment and may use, for example, ametal material, an ionized metal material, an alloy material, a metalink material that is in a colloid state in a predetermined liquid, andtransparent metal oxide.

In detail, for example, the metal material may use at least one oflithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li),calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag),platinum (Pt), gold (Au), nickel (Ni), copper (Cu), barium (Ba), silver(Ag), indium (In), ruthenium (Ru), lead (Pd), rhodium (Rh), iridium(Ir), osmium (Os) and cesium (Cs). Also, carbonate (C), conductivepolymers, or combinations thereof may be used for the metal material.

The transparent metal oxide may include at least one of indium tin oxide(ITO), fluorine-doped tin oxide (FTO), antimony tin oxide (ATO) andaluminum doped zinc oxide (AZO).

Although the ITO is generally used as a material that forms the anode110, the ITO may be used as a material for forming the cathode 140 andmay form the transparent cathode 140 in an inverted solar cellstructure.

The LED 100 according to an embodiment may simultaneously perform thefunctionality of hole injection and electron injection by including theCGJ layer 120 capable of performing the hole injection or electroninjection functionality without including a separate hole injectionlayer or electron injection layer.

The CGJ layer 120 according to an embodiment may be formed using asolution process. The solution process may enable a large-scale process,may save a process time, and may relieve constraints on semiconductorproperties of the anode 110 and the cathode 140.

The LED 100 according to an embodiment may include the CGJ layer 120 ina layer-by-layer structure in which the n-type oxide 121 and the p-typeoxide 122 are sequentially stacked on at least one surface of the lightemitting layer 132.

In detail, the CGJ layer 120 may be formed between the light emittinglayer 132 and the cathode 140 as illustrated in FIG. 1B, and may beformed between the light emitting layer 132 and the anode 110 asillustrated in FIG. 1C.

Depending on embodiments, as illustrated in FIG. 1D, the CGJ layer 120may be formed on both surfaces of the light emitting layer 132, that is,between the light emitting layer 132 and the cathode 140 and between thelight emitting layer 132 and the anode 110.

In the CGJ layer 120, the n-type oxide 121 and the p-type oxide 122 areformed in a layer-by-layer structure. Therefore, electrons may betunneled from highest occupied molecular orbital (HOMO) to lowestunoccupied molecular orbital (LUMO) due to band bending.

Such tunneling may supply charge carriers (electrons or holes) to theLED 100. Referring to FIG. 1B, charge carriers supplied from the CGJlayer 120 present between the light emitting layer 132 and an intagliomay be electrons.

The effect similar to the effect of containing a metal betweenelectrodes, for example, the cathode 140 and the anode 110 may beachieved in that the CGJ layer 120 supplies charge carriers.

Injecting electrons from the cathode 140 may decisively depend on a workfunction of a material of the cathode 140. Here, cleaning the cathode140 or preparing the surface of the cathode 140 before forming thecathode 140 may have a strong impact on the work function of the cathode140, which may lead to causing a strong impact on the injection barrier.

Accordingly, the CGJ layer 120 formed in the LED 100 in the structure ofFIG. 1B may improve charge injection properties of the LED 100 byseparating the charge injection properties of the LED 100 from the workfunction of the cathode 140.

If the n-type oxide 121 and the p-type oxide 122 constituting the CGJlayer 120 according to an embodiment have the band gap energy of 3.0 eVor more, any type of materials may be used.

If the n-type oxide 121 and the p-type oxide 122 have the band gapenergy of less than 3.0 eV, charge generation junction (CGJ) isimpossible due to an insufficient band gap.

The n-type oxide 121 according to an embodiment is a material thatincludes zinc oxide and, depending on embodiments, may be zinc oxidedoped with a dopant.

The dopant may include at least one of cesium (Cs), lithium (Li),aluminum (Al), magnesium (Mg), indium (In), and gallium (Ga).

The dopant may be contained in the zinc oxide at 0.1 atomic % to 50atomic %.

If the content of the dopant is 0.1 atomic % or less, the sufficientdoping effect may not be exhibited in that a small amount is added.Also, if the content of the dopant exceeds 50 atomic %, properties ofthe n-type oxide 121 may be degraded and charge generation may decrease.

The n-type oxide 121 may be generated in at least one of a sol-gel formand a nanoparticle form.

Depending on embodiments, the p-type oxide 122 used for the CGJ layer120 may use PEDOT:PSS, which is generally used, or PEDOT:PSS mixed withadditives. The additives may be a material that includes at least one ofgraphene oxide (GO), carbon nanotube (CNT), vanadium oxide (V₂O₅),tungsten oxide (WO₃), and polyoxyethylene tridecyl ether (PTE).

The p-type oxide 122 used for the CGJ layer 120 according to anembodiment may be a material represented by the following Formula.Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula]

Here, 0.2<x<1.5.

PEDOT:PSS that is conventionally used for the p-type oxide 122 is acidicand thus, causes damage on the electrode surface and reacts with thezinc oxide contained in the n-type oxide 121 to degrade the chargegeneration and transport properties of the CGJ layer 120 and electricalperformance of the LED 100.

Dissimilar to PEDOT:PSS, the p-type oxide 122 represented by the aboveFormula does not damage the anode 110 or the cathode 140 and does notreact to the n-type oxide 121, which may lead to improving the chargegeneration and transport properties and to allowing the LED 100 to havethe excellent electrical performance.

The p-type oxide 122 may be formed by manufacturing a precursor solutionthat includes Cu, S, M (M is one more compounds selected from SnO, ITO,IZTO, IGZO, and IZO), and Ga, by applying the precursor solution overthe substrate on which the anode 110 is formed to form a coating layer,and then by thermally treating the coating layer.

Depending on embodiments, referring to FIG. 1B, when the CGJ layer 120is formed between the light emitting layer 132 and the anode 110, theLED 100 according to an embodiment may include an electron transportlayer between the light emitting layer 132 and the cathode 140.

The electron transport layer is formed between the light emitting layer132 and the cathode 140 and serves to easily transport electronsgenerated from the cathode 140 to the light emitting layer 132.

The electron transport layer may include at least one of fullerene(C60), fullerene derivatives, perylene, TPBi(2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phynyl-1-H-benzimidazole)),polybenzimidazole (PBI), and PTCBI (3,4,9,10-perylene-tetracarboxylicbis-benzimidazole), naphthalene diimide (NDI) and derivatives thereof,TiO₂, SnO₂, ZnO, ZnSnO₃,2,4,6-Tris(3-(pyrimidin-5-yl)phenyl)-1,3,5-triazine,8-Hydroxyquinolinolato-lithium,1,3,5-Tris(1-phenyl-1Hbenzimidazol-2-yl)benzene,6,6′-Bis[5-(biphenyl-4-yl)-1,3,4-oxadiazo-2-yl]-2,2′-bipyridyl,4,4′-Bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl(BTB), rubidiumcarbonate (Rb₂CO₃), and rhenium (VI) oxide (ReO₃). The fullerenederivatives may be PCBM ((6,6)-phenyl-C61-butyric acid-methylester) orPCBCR ((6,6)-phenyl-C61-butyric acid cholesteryl ester). However, it isprovided as an example only and the disclosure is not limited to thematerials.

Here, in an inverted structure, TiO₂-based or Al₂O₃-based porousmaterials may be generally used for the electron transport layer, but itis provided as an example only.

The electron transport layer according to an embodiment may beconfigured as the n-type oxide 121.

Depending on embodiments, the n-type oxide 121 may include, desirably,zinc oxide (ZnO), more desirably, dopant-doped zinc oxide.

The LED 100 may have charge injection properties, depending on a workfunction of a metal. In the case of the conventional LED 100 including acharge injection layer configured as a single p-type oxide 122 or n-typeoxide 121, charge injection may not be smoothly performed due to theenergy barrier by a work function of upper/lower electrodes, forexample, the anode 110 or the cathode 140.

However, when the CGJ layer 120 is formed on the LED 100 according to anembodiment, charge is generated on the interface between the p-typeoxide 122 and the n-type oxide 121. Therefore, although metals havingdifferent work functions are used for electrodes, there is no effect onthe energy barrier by the work functions.

That is, since the CGJ layer 120 according to an embodiment allowscharge to be generated on the interface between the p-type oxide 122 andthe n-type oxide 121, charge generation and injection may be stabilized.

Hereinafter, a current flow of a CGJ layer according to an embodiment isdescribed.

FIG. 2A illustrates a current flow of a CGJ layer in forward bias of anLED according to an embodiment, and FIG. 2B illustrates a current flowof a CGJ layer in reverse bias of an LED according to an embodiment.

FIGS. 2A and 2B illustrate a current flow in forward bias and reversebias when the p-type oxide 122 of the CGJ layer according to anembodiment is lithium (Li)-doped zinc oxide (LZO) and the n-type oxide121 of the CGJ layer is Cu₂SnS₃—Ga₂O₃.

Specific examples of manufacturing the CGJ layer will be described withthe following property evaluation.

Referring to FIG. 2A, in the forward bias, holes and electrons arerespectively injected from the anode 110 and the cathode 140 andtransported through a valence band maximum (VBM) of Cu₂SnS₃—Ga₂O₃ and aconduction band minimum (CBM) of LZO. The holes and the electrons arerecombined on the interface between LZO and Cu₂SnS₃—Ga₂O₃.

Referring to FIG. 2B, on the contrary, in the reverse bias, electronsmove from the VBM of Cu₂SnS₃—Ga₂O₃ to the CBM of LZO and holes areformed at the VBM of Cu₂SnS₃—Ga₂O₃.

Holes and electrons are generated on the interface between LZO andCu₂SnS₃—Ga₂O₃ constituting the CGJ layer, and the generated holes andelectrons move to electrodes, for example, the anode 110 and the cathode140, through the reverse electric field.

Here, forward current is caused by charge injected from the electrodes,for example, the anode 110 and the cathode 140, and reverse current iscaused by charge generated in the CGJ layer.

FIG. 3 is a graph showing current-voltage properties of a CGJ layer inforward bias and reverse bias of an LED according to an embodiment.

Referring to FIG. 3, since the reverse current density indicated isalmost identical to the forward current density, it can be seen that theeffective charge generation is possible in a CGJ layer according to anembodiment.

The LED according to an embodiment includes the CGJ layer having theexcellent charge generation and transport capability and thus, may havethe current efficiency (CE) of 1 cd/A to 100 cd/A and the externalquantum efficiency (EQE) of 5% to 25%.

The LED according to an embodiment may be a multi-stacked LED thatincludes at least two light emitting layers.

In detail, the multi-stacked LED according to an embodiment may includean anode, a hole transport layer, at least two light emitting layers,and a cathode.

The CGJ layer formed in a layer-by-layer structure in which an n-typeoxide and a p-type oxide are sequentially stacked may be includedbetween the at least two light emitting layers.

Here, the hole transport layer and the light emitting layer may bereferred to as an EL unit. The multi-stacked LED according to anembodiment may include at least two EL units.

Therefore, the CGJ layer formed in the multi-stacked LED according to anembodiment may be formed between the at least two EL units.

Depending on embodiments, the CGJ layer formed in the multi-stacked LEDaccording to an embodiment may be selectively formed between the anodeand the EL unit or between the cathode and the EL unit.

In the CGJ layer formed in the multi-stacked LED according to anembodiment, the n-type oxide and the p-type oxide may have the band gapenergy of 3.0 eV or more.

In the CGJ layer formed in the multi-stacked LED according to anembodiment, the n-type oxide may include zinc oxide and, depending onembodiments, may be zinc oxide doped with a dopant.

The dopant may include at least one of cesium (Cs), lithium (Li),aluminum (Al), magnesium (Mg), indium (In), and gallium (Ga).

In the CGJ layer formed in the multi-stacked LED according to anembodiment, the p-type oxide may be a material represented by thefollowing Formula.Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula]

Here, 0.2<x<1.5.

For example, the n-type oxide may be LZO and the p-type oxide may beCu₂SnS₃—Ga₂O₃.

The light emitting layer included in the multi-stacked LED according toan embodiment may include one of a quantum dot, an oxide layer, anitride layer, a semiconductor layer, an organic compound layer, aninorganic compound layer, a phosphor layer, and a dye layer.

Detailed description related to the anode, the CGJ layer, the EL unit,and the cathode included in the multi-stacked LED according to anembodiment is made above with reference to FIGS. 1A to 3 and thus,further description is omitted.

Hereinafter, a structure of a multi-stacked LED according to anembodiment is further described with reference to FIGS. 4A and 4B.

FIGS. 4A and 4B are cross-sectional views illustrating a detailedstructure of a multi-stacked LED according to an embodiment.

Referring to FIG. 4A, a multi-stacked LED 200 according to an embodimentmay include two EL units 230, and may be formed in a stacked structurein sequential order of anode 210-CGJ layer 220-EL unit 230-CGJ layer220-EL unit 230-CGJ layer 220-cathode 240.

The CGJ layer 220 formed between two EL units 230 includes an n-typeoxide 221 formed on the EL unit 230 provided on the bottom surface ofthe CGJ layer 220 and a p-type oxide 222 formed on the EL unit 230provided on the top surface of the CGJ layer 220 to enable switchingbetween holes and electrons for charge transport.

Referring to FIG. 4B, the multi-stacked LED 200 according to anembodiment may include three EL units 230, may be in a stacked structurein sequential order of anode 210-CGJ layer 220-EL unit 230-CGJ layer220-EL unit 230-CGJ layer 220-EL unit 230-CGJ layer 220-cathode 240.

Likewise, even in the case of the multi-stacked LED 200 that includes ELunits 230, the CGJ layer 220 includes the n-type oxide 221 formed on theEL unit 230 provided on the bottom surface of the CGJ layer 220 and thep-type oxide 222 formed on the EL unit 230 provided on the top surfaceof the CGJ layer 220 to enable switching between hole and electrontransportation.

The multi-stacked LED 200 according to an embodiment may be formed in atandem structure that includes at least two light emitting layers andthus, may achieve high performance at low cost.

In the multi-stacked LED 200 according to an embodiment, charge may begenerated on the interface between the n-type oxide 221 and the p-typeoxide 222. Therefore, although metals having different work functionsare used for electrodes, there is no effect on the energy barrier by thework functions.

That is, in the multi-stacked LED 200 according to an embodiment, chargegeneration occurs on the interface between the n-type oxide 221 andp-type oxide 222 due to the CGJ layer 220 formed between the lightemitting layers. Therefore, charge generation and injection may bestabilized.

The multi-stacked LED 200 according to an embodiment may include aplurality of CGJ layers 220 having excellent charge generation andtransport capability and thus, may have the current efficiency (CE) of 3cd/A to 300 cd/A and the external quantum efficiency (EQE) of 15% to75%.

Hereinafter, a process of manufacturing an LED according to anembodiment is described.

FIG. 5 is a flowchart illustrating a process of manufacturing an LEDaccording to an embodiment.

Referring to FIG. 5, a method of manufacturing an LED according to anembodiment includes operation S110 of forming an anode on a substrate,operation S120 of forming a hole transport layer on the anode, operationS130 of forming a light emitting layer on the hole transport layer,operation S140 of forming a cathode on the light emitting layer, andoperation S150 of forming a CGJ layer on at least one surface of thelight emitting layer.

Depending on embodiments, by performing operation S150 after operationS110, the LED may be manufactured such that the CGJ layer may be formedbetween the anode and the light emitting layer. Alternatively, byperforming operation S150 after operation S130, the LED may bemanufactured such that the CGJ layer may be formed between the lightemitting layer and the cathode.

Alternatively, by performing operation S150 after operation S110 oroperation S130, the LED may be manufactured such that the CGJ layer maybe formed between the light emitting layer and the anode and between thelight emitting layer and the cathode.

The method of manufacturing an LED according to an embodiment differsfrom the LED described above with reference to FIGS. 1A to 5 only interms of categories and thus, repeated description is omitted.

In operation S110, a material for the anode may be formed on thesubstrate using, for example, a thermal evaporation, an e-beamevaporation, a radio frequency (RF) sputtering, a magnetron sputtering,a vacuum deposition, or a chemical vapor deposition. However, it isprovided as an example only.

Depending on embodiments, in operation S110, the anode may be formed onthe substrate using conventional technology, for example, a depositionscheme such as a chemical vapor deposition (CVD) or a scheme of printingpaste metal ink in which metal flakes and particles are mixed with abinder. Here, any methods capable of forming an electrode may apply.

Examples of a material for the anode used in operation S110 aredescribed above with reference to FIGS. 1A to 1D and thus, furtherdescription is omitted.

In operation S120, the hole transport layer may be formed by applying amaterial capable of forming the hole transport layer on the anodethrough a spray coating, a spin coating, an ultra-spray coating, anelectrospun coating, a slot dye coating, a gravure coating, a barcoating, a roll coating, a dip coating, a shear coating, a screenprinting, an inkjet printing, or a nozzle printing. However, it isprovided as an example only.

Examples of the material for the hole transport layer used in operationS120 are described above with reference to FIGS. 1A to 1D and thus,further description is omitted.

In operation 130, the light emitting layer may be formed by applying amaterial capable of forming the light emitting layer through a vacuumdeposition, a chemical vapor deposition, a physical vapor deposition, anatomic layer deposition, a metal organic chemical vapor deposition, aplasma-enhanced chemical vapor deposition, a molecular beam epitaxy, ahydride vapor phase epitaxy, a sputtering, a spin coating, a dipcoating, and a zone casting.

Examples of the material for the light emitting layer used in operationS130 may include a quantum dot, organic compound, oxide, nitride, asemiconductor material, inorganic compound, a phosphor material, anddye, which are described above with reference to FIGS. 1A to 1D andthus, further description is omitted.

In operation S140, if the cathode is a transparent metal oxideelectrode, the cathode may be formed by applying a sol-gel, a spraypyrolysis, a sputtering, an atomic layer deposition (ALD) or an e-beamevaporation.

The cathode may be formed using a deposition scheme, such as a chemicalvapor deposition (CVD) or a scheme of printing paste metal ink in whichmetal flakes or particles are mixed with a binder. Any methods capableforming an electrode may apply.

In operation S150, the CGJ layer may be formed on at least one surfaceof the light emitting layer using a solution process.

The CGJ layer may be formed on at least one surface of the lightemitting layer in a layer-by-layer structure in which the n-type oxideand the p-type oxide are sequentially stacked.

The n-type oxide may include zinc oxide and, depending on embodiments,may be zinc oxide doped with a dopant.

The p-type oxide may be a material represented by the following Formula.Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula]

Here, 0.2<x<1.5.

Depending on embodiments, the n-type oxide may be LZO and the p-typeoxide may be Cu₂SnS₃—Ga₂O₃.

A process of forming the CGJ layer is further described with referenceto FIG. 6.

FIG. 6 illustrates a process of manufacturing a CGJ layer according toan embodiment.

Referring to FIG. 6, a method of manufacturing a CGJ layer forms ann-type oxide 121 by applying an n-type oxide solution 1 over a substrate10.

The n-type oxide solution 1 includes the n-type oxide 121 and mayinclude zinc oxide or zinc oxide doped with a dopant.

A solvent available for the n-type oxide solution 1 may be prepared bymixing at least one of 5 to 50% by volume of 2-methoxyethanol,acetonitrile, DI water, alcohol, cyclohexane, toluene, and an organicsolvent with ethylene glycol.

The n-type oxide 121 may be formed using one solution process selectedfrom a spin-coating, a slit dye coating, an ink-jet printing, a spraycoating, and a dip coating.

Desirably, the n-type oxide 121 may be formed using a spin coating witha centrifugal force applied to a solution by dropping a predeterminedamount of solution over the substrate 10 and then rotating the substrate10 at a high speed.

Subsequently, a p-type oxide 122 is formed by applying a p-type oxidesolution 2 over the top surface of the n-type oxide 121.

The p-type oxide solution 2 includes the p-type oxide 122 and may be amaterial represented by the above Formula.

A solvent available for the p-type oxide solution 2 may be prepared bymixing at least one of 5 to 50% by volume of 2-methoxyethanol,acetonitrile, DI water, alcohol, cyclohexane, toluene, and an organicsolvent with ethylene glycol.

Similar to the n-type oxide 121, the p-type oxide 122 may be formedusing one solution process selected from a spin-coating, a slit dyecoating, an ink-jet printing, a spray coating, and a dip coating.

Subsequently, heat treatment or ultraviolet (UV)/ozone treatment may beperformed on the substrate 10 on which the n-type oxide 121 and thep-type oxide 122 are formed.

The heat treatment may be performed for 10 minutes to 60 minutes at 150°C. to 250° C.

The UV/ozone treatment may be performed for 30 seconds to 5 minutes.

Although FIG. 6 illustrates that the CGJ layer according to anembodiment is formed on the substrate 10, the CGJ layer may be formed onthe anode or the light emitting layer to be in contact with at least onesurface of the light emitting layer through the aforementioned process.

The CGJ layer may be formed through the solution process, which mayenable a large-scale process at a low temperature, may save a processtime, and may relieve constraints on semiconductor properties of upperand lower electrodes, for example, the anode and the cathode.

Referring again to FIG. 5, the method of manufacturing an LED accordingto an embodiment may manufacture a multi-stacked LED by repeatedlyperforming operations S130 and S150.

In detail, the method of manufacturing an LED according to an embodimentmay manufacture the multi-stacked LED including at least two lightemitting layers in which the CGJ layer is formed between the at leasttwo light emitting layers by repeatedly performing operations S130 andS150.

The method of manufacturing an LED according to an embodiment mayrepeatedly perform operations S120, S130, and S150 to form at least twoEL units including the hole transport layer and the light emitting layerand to form the CGJ layer between the at least two EL units.

Hereinafter, properties of an LED according to embodiments are describedwith reference to FIGS. 7 to 17B.

Embodiment 1

An ITO glass substrate with sheet resistance of 9 Ω/sq was cleaned bysequentially ultrasonic treating each of acetone, methanol, andisopropanol for 15 minutes.

Next, for a spin coating process, the ITO substrate was moved to a glovebox filled with N₂.

A hole injection layer was formed on the ITO substrate by spin-coatingCu₂SnS₃—Ga₂O₃ at 4000 rpm and then baking the same for 60 minutes at 200

.

A hole transport layer was formed on the hole injection layer byspin-coating poly(9-vinylcarbazole) (PVK) at 4000 rpm and then bakingthe same for 10 minutes at 160

.

A light emitting layer was formed on the hole transport layer byspin-coating a solution including a quantum dot at 2000 rpm and thenbaking the same for 10 minutes at 190

.

A blue light emitting layer is formed with a solution in which CdS/ZnSis dissolved in toluene at the concentration of 10 mg/mL, a green lightemitting layer is formed in a solution in which CdZnSeS/ZnS is dissolvedin toluene at the concentration of 10 mg/mL, and a red light emittinglayer is formed in a solution in which a CdZnSeS/ZnS is dissolved intoluene at the concentration of 10 mg/mL.

An electron transport layer was formed on the light emitting layer byspin-coating LZO at 2000 rpm and then baking the same for 30 minutes at200

.

Accordingly, an LED, that is, a quantum dot LED (QLED) was manufacturedby depositing 100 nm of Al through thermal evaporation under high vacuumand by forming a cathode on the electron transport layer.

Embodiment 2

An LED was manufactured in the same manner as in Embodiment 1, exceptfor forming a CGJ layer on a light emitting layer by spin-coating LZO asan n-type oxide at 2000 rpm and baking the same for 30 minutes at 200

and then by spin-coating Cu₂SnS₃—Ga₂O₃ as a p-type oxide at 4000 rpm andbaking the same for 60 minutes at 200

.

Embodiment 3

An LED was manufactured in the same manner as in Embodiment 1, exceptfor forming a CGJ layer on an anode by spin-coating LZO as an n-typeoxide at 2000 rpm and baking the same for 30 minutes at 200

and then by spin-coating Cu₂SnS₃—Ga₂O₃ as a p-type oxide at 4000 rpm andbaking the same for 60 minutes at 200

.

Embodiment 4

An LED was manufactured in the same manner as in Embodiment 1, exceptfor forming a CGJ layer on an anode and a light emitting layer byspin-coating LZO as an n-type oxide at 2000 rpm and baking the same for30 minutes at 200

and then by spin-coating Cu₂SnS₃—Ga₂O₃ as a p-type oxide at 4000 rpm andbaking the same for 60 minutes at 200

.

Embodiment 5

A multi-stacked LED, for example, a 2-stacked LED was manufactured inthe same manner as in Embodiment 1, except for forming a CGJ layer afterforming a hole transport layer and a light emitting layer between theCGJ layer and a cathode in Embodiment 4.

Embodiment 6

A multi-stacked LED, for example, a 3-stacked LED was manufactured inthe same manner as in Embodiment 1, except for forming a CGJ layer afterforming a hole transport layer and a light emitting layer between theCGJ layer and a cathode and also emitting white light by forming blue,green, and red light emitting layers on the light emitting layer inEmbodiment 5.

Embodiment 7

An LED, for example, an organic LED (OLED) was manufactured in the samemanner as in Embodiment 1, except for forming a CGJ layer on an anode bysequentially stacking LZO as an n-type oxide and Cu₂SnS₃—Ga₂O₃ as ap-type oxide, not a hole injection layer.

Embodiment 8

An LED (e.g., OLED) was manufactured in the same manner as in Embodiment1, except for forming a CGJ layer on an anode by sequentially stackingCu₂SnS₃—Ga₂O₃ as a p-type oxide and LZO as an n-type oxide, not a holeinjection layer.

Comparative Example 1

An LED (e.g., OLED) was manufactured in the same manner as in Embodiment1, except for using Cu₂SnS₃—Ga₂O₃ as a hole injection layer, TCTA/NPB asa hole transport layer, TCTA:TPBi:Ir (ppy)₃ as a light emitting layer,TPBi as an electron transport layer, and LiF/Al as a cathode.

Comparative Example 2

An LED (e.g., OLED) was manufactured in the same manner as in Embodiment1, except for using LZO and MLZO (ZnO doped with Mg and Li) as a holeinjection layer, PEIE:Rb₂CO₃ as a hole transport layer, TCTA:TPBi:Ir(ppy)₃ as a light emitting layer, TCTA/NPB as an electron transportlayer, and HAT-CN as an electron injection layer.

Property Evaluation

1. Properties of CGJ Layer

FIG. 7 is a graph showing optical band gap properties of an n-type oxideand a p-type oxide of an LED according to an embodiment.

Referring to FIG. 7, it can be seen that LZO, i.e., the n-type oxide,and Cu₂SnS₃—Ga₂O₃, that is, the p-type oxide, which constitute the CGJlayer formed in the above Embodiment 1 to Embodiment 8, have the opticalband gap of 3.37 eV and 3.82 eV, respectively.

FIG. 8 is a graph showing transmittance of a CGJ layer according to anembodiment.

Referring to FIG. 8, it can be seen that the CGJ layer formed in theabove Embodiment 1 to Embodiment 8 has the transmittance of about 93%,which is significantly high.

That is, since the transmittance of the CGJ including the n-type oxideand the p-type oxide according to an embodiment is very high, it ispossible to further transmit light emitted from the LED and therebyallow more light to be emitted.

2. Electrical Properties of QLED

Hereinafter, electrical properties of the LED (QLED) according to theabove Embodiment 1 to Embodiment 4 were evaluated.

FIG. 9A is a graph showing a current-voltage curve of an LED accordingto an embodiment.

Referring to FIG. 9A, it can be seen that, based on the same voltagecondition, Embodiment 4 (Device D) exhibits the largest current densityand the current density decreases in order of Embodiment 3 (Device C),Embodiment 2 (Device B), and Embodiment 1 (Device A).

That is, since the largest current density is achieved in Embodiment 4in which the CGJ layer is formed on each of both surfaces of the lightemitting layer, it is desirable to form the CGJ layer on each of bothsurfaces of the light emitting layer, rather than on one surface of thelight emitting layer, to manufacture a high efficiency LED.

Also, it can be seen that the difference in the current density betweenEmbodiment 3 and Embodiment 4 and the difference in the current densitybetween Embodiment 1 and Embodiment 2 are almost same under the samevoltage.

Further, it can be seen that the difference in the current densitybetween Embodiment 2 and Embodiment 3 is greater than the difference inthe current density between Embodiment 3 and Embodiment 4 or thedifference in the current density between Embodiment 1 and Embodiment 2under the same voltage.

Embodiment 2 relates to the LED in which the CGJ layer is formed on thelight emitting layer and Embodiment 3 relates to the LED in which theCGJ layer is formed on the anode. It can be seen that the currentdensity of the LED in which the CGJ layer is formed on the anode isrelatively greater and thus, higher efficiency is achieved.

In the case of the quantum dot LED (QLED) using the ZnO electrontransport layer and the PVK hole transport layer, the electron mobility(˜10⁻⁴ cm² v⁻¹ s⁻¹) of ZnO is significantly great compared to the holemobility (˜10⁻⁶ cm² v⁻¹ s⁻¹) of PVK.

The great difference between the electron mobility and the hole mobilitycauses charge imbalance in the quantum dot light emitting layer.

In Embodiment 3, it can be seen that the current density is high due tothe improvement in the hole mobility by the CGJ layer and the balancedcharge injection.

That is, according to data of Embodiment 2 and Embodiment 3, theefficiency of the LED may vary based on a location at which the CGJlayer is formed.

Also, it can be seen that turn-on voltages and driving voltages ofEmbodiment 2 to Embodiment 4 are higher than those of Embodiment 1.

Through this, it is possible to verify efficient charge injectionproperties of the CGJ layer formed in Embodiment 2 to Embodiment 4.

Accordingly, to improve the efficiency of the LED, it may be desirableto form the CGJ layer on the anode. Also, to maximize the efficiency ofthe LED, the CGJ layer may be formed on each of both surfaces of thelight emitting layer.

FIG. 9B is a graph showing a luminance-voltage curve of an LED accordingto an embodiment.

Referring to FIG. 9B, it can be seen that luminance of Embodiment 3(Device C) and Embodiment 4 (Device D) is greater than that ofEmbodiment 1 (Device A) and Embodiment 2 (Device B).

In detail, the luminance of Embodiment 4 has a slightly greater valuethan the luminance of Embodiment 3 and the luminance of Embodiment 2 hasa value almost similar to the luminance of Embodiment 1. Here, if thevoltage is about 6V or more, the luminance of Embodiment 2 has a valuegreater than the luminance of Embodiment 1.

That is, it can be known that the luminous efficiency of Embodiment 4 inwhich the CGJ layer is formed on each of both surfaces of the lightemitting layer is more excellent that that of Embodiment 2 andEmbodiment 3 in which the CGJ layer is formed on only one surface of thelight emitting layer.

Here, a great difference between luminance values of Embodiment 2 andEmbodiment 3 is caused by a different formation location of the CGJlayer.

Embodiment 3 exhibits the improved hole mobility by the CGJ layer andthe balanced charge injection and accordingly, has the luminance greaterthan that of Embodiment 2.

As described above with reference to FIG. 9A, a current density valuevaries based on a formation location of the CGJ layer, which causes theluminance value to differ.

FIG. 9C is a graph showing a current efficiency-luminance curveaccording to an embodiment.

Referring to FIG. 9C, it can be seen that the current efficiency ofEmbodiment 2 to Embodiment 4 is greater than that of Embodiment 1.

That is, the CGJ layer formed in Embodiment 2 to Embodiment 4 mayimprove the current efficiency of the LED by efficiently transportingholes and electrons.

Also, it can be seen that Embodiment 4 does not show a great change inthe current efficiency compared to Embodiment 2 and Embodiment 3although the luminance increases. When the CGJ layer is formed on eachof both surfaces of the light emitting layer rather than on one surfaceof the light emitting layer, the change in the current efficiency issmall, which may lead to improving the durability of the LED.

Charge imbalance is likely to occur at high luminance. In Embodiment 2and Embodiment 4 that relate to the LED in which the CGJ layer is formedon the cathode, charge injection balance is relatively excellent even athigh luminance and a high current efficiency value may be acquiredaccordingly.

FIG. 9D is a graph showing a power efficiency-luminance curve accordingto an embodiment.

Referring to FIG. 9D, it can be seen that the power efficiency ofEmbodiment 2 to Embodiment 4 in which the CGJ layer is formed is greaterthan that of Embodiment 1.

That is, the CGJ layer formed in Embodiment 2 to Embodiment 4 maythereby improve the power efficiency of the LED by efficientlytransporting holes and electrons.

Also, it can be seen that Embodiment 4 does not show a great decrease inthe power efficiency compared to Embodiment 2 and Embodiment 3 althoughthe luminance increases. When the CGJ layer is formed on each of bothsurfaces of the light emitting layer rather than on one surface of thelight emitting layer, the change in the power efficiency is small, whichmay lead to improving the durability of the LED.

Charge imbalance is likely to occur at high luminance. In Embodiment 2and Embodiment 4 that relate to the LED in which the CGJ layer is formedon the cathode, charge injection balance is relatively excellent even athigh luminance and a high power efficiency value may be acquiredaccordingly.

3. Electrical Properties of Multi-Stacked QLED

Hereinafter, electrical properties of a multi-stacked LED were evaluatedby comparing electrical properties between the LED according toEmbodiment 4 and the multi-stacked LED according to Embodiment 5 andEmbodiment 6.

FIG. 10A is a graph showing a current-voltage curve of a blue LED and amulti-stacked blue LED according to an embodiment, FIG. 10B is a graphshowing a luminance-voltage curve of a blue LED and a multi-stacked blueLED according to an embodiment, FIG. 10C is a graph showing a currentefficiency-luminance curve of a blue LED and a multi-stacked blue LEDaccording to an embodiment, and FIG. 10D is a graph showing an externalquantum efficiency (EQE)-luminance curve of a blue LED and amulti-stacked blue LED according to an embodiment.

Referring to FIGS. 10A to 10D, it can be seen that Embodiment 5(2-stack) and Embodiment 6 (3-stack) have the turn-on voltage of 9.06 Vand 13.71 V, respectively.

Also, it can be seen that Embodiment 5 of blue and Embodiment 6 have themaximum current efficiency (CE) of 2.17 cd/A and 3.23 cd/A,respectively, and have the EQE of 9.89% and 14.70%, respectively.

The maximum current efficiency and the maximum EQE values of Embodiment5 and Embodiment 6 are almost twice or three times greater thanEmbodiment 4 (Single) having the turn-on voltage of 4.37 V, the maximumcurrent efficiency of 1.13 cd/A, and the maximum EQE of 5.12%.

Also, it can be seen that current density and luminance values ofEmbodiment 5 and Embodiment 6 are greater than those of Embodiment 4.

Accordingly, it can be known that the charge transport efficiency ofEmbodiment 5 and Embodiment 6 is which a more number of CGJ layers areformed is more excellent than that of Embodiment 4.

Comparing data between Embodiment 5 and Embodiment 6, current density,luminance, current efficiency, and EQE values of Embodiment 6 (3-stack)are greater than those of Embodiment 5 (2-stack).

Through this, it can be known that the charge transport efficiency ofEmbodiment 6 in which a more number of CGJ layers are formed is greaterthan that of Embodiment 5.

FIG. 11A is a graph showing a current-voltage curve of a green LED and amulti-stacked green LED according to an embodiment, FIG. 11B is a graphshowing a luminance-voltage curve of a green LED and a multi-stackedgreen LED according to an embodiment, FIG. 11C is a graph showing acurrent efficiency-luminance curve of a green LED and a multi-stackedgreen LED according to an embodiment, and FIG. 11D is a graph showing anEQE-luminance curve of a green LED and a multi-stacked green LEDaccording to an embodiment.

Referring to FIGS. 11A to 11D, it can be seen that the operating voltageof Embodiment 5 and Embodiment 6 has a value greater by twice or threetimes than that of Embodiment 4 at a specific luminance value.

Embodiment 5 shows the high current efficiency of 93.42 cd/A and thehigh EQE of 28.94%, which are almost twice greater than the currentefficiency of 50.20 cd/A and the EQE of 15.61% of Embodiment 4.

Further, Embodiment 6 shows the high current efficiency of 143.92 cd/Aand the high EQE of 44.69%, which are greater by three times than thoseof Embodiment 4.

Since Embodiment 6 (3-stack) is implemented as three single LEDs each inwhich the CGJ layer using LZO/Cu₂SnS₃—Ga₂O₃ is formed, the above resultsmay be achieved.

Also, it can be seen that current density and luminance values ofEmbodiment 5 and Embodiment 6 are greater than those of Embodiment 4.

Accordingly, it can be known that the charge transport efficiency ofEmbodiment 5 and Embodiment 6 in which a more number of CGJ layers areformed is greater than that of Embodiment 4.

Also, comparing data between Embodiment 5 and Embodiment 6, it can beseen that current density, luminance, current efficiency, and EQE valuesof Embodiment 6 (3-stack) are greater than those of Embodiment 5(2-stack).

Through this, it can be known that the charge transport efficiency ofEmbodiment 6 in which a more number of CGJ layers are formed is greaterthan that of Embodiment 5.

FIG. 12A is a graph showing a current-voltage curve of a red LED and amulti-stacked red LED according to an embodiment, FIG. 12B is a graphshowing a luminance-voltage curve of a red LED and a multi-stacked redLED according to an embodiment, FIG. 12C is a graph showing a currentefficiency-luminance curve of a red LED and a multi-stacked red LEDaccording to an embodiment, and FIG. 12D is a graph showing anEQE-luminance curve of a red LED and a multi-stacked red LED accordingto an embodiment.

Referring to FIGS. 12A to 12D, it can be seen that Embodiment 4 has aturn-on voltage value of 2.44 V, Embodiment 5 has a turn-on voltagevalue of 5.07 V, and Embodiment 6 has a turn-on voltage value of 8.12 V.

Also, it can be seen that Embodiment 4 has the maximum currentefficiency of 11.44 cd/A, Embodiment 5 has the maximum currentefficiency of 22.11 cd/A, and Embodiment 6 has the maximum currentefficiency of 33.15 cd/A.

Also, it can be seen that Embodiment 5 and Embodiment 6 respectivelyhave the maximum EQE of 15.57% and 23.34%, which are greater than 8.06%that is the maximum EQE of Embodiment 4.

Also, it can be seen that current density and luminance values ofEmbodiment 5 and Embodiment 6 are greater than those of Embodiment 4.

Accordingly, it can be known that the charge transport efficiency ofEmbodiment 5 and Embodiment 6 in which a more number of CGJ layers areformed is greater than that of Embodiment 4.

Also, comparing data between Embodiment 5 and Embodiment 6, it can beseen that current density, luminance, current efficiency, and EQE valuesof Embodiment 6 (3-stack) are greater than those of Embodiment 5(2-stack).

Through this, it can be known that the charge transport efficiency ofEmbodiment 6 in which a more number of CGJ layers are formed is greaterthan that of Embodiment 5.

Accordingly, it can be known that the blue, green, and red multi-stackedLEDs according to FIGS. 10A to 10D, 11A to 11D, and 12A to 12D mayachieve the excellent electrical performance through the high-efficiencycharge generation and transport of the CGJ layer.

FIG. 13A is a graph showing a current-voltage curve of a multi-stackedwhite LED according to an embodiment, FIG. 13B is a graph showing aluminance-voltage curve of a multi-stacked white LED according to anembodiment, FIG. 13C is a graph showing a current efficiency-luminancecurve of a multi-stacked white LED according to an embodiment, and FIG.13D is a graph showing an EQE-luminance curve of a multi-stacked whiteLED according to an embodiment.

Referring to FIGS. 13A to 13D, it can be seen that white Embodiment 6has a turn-on voltage value of 11.01 V, which is almost identical to asum of turn-on voltage values of Embodiment 4 of blue, green, and red.

Through this, it can be known that the CGJ layer may effectively connectblue, green, and red EL units.

Due to such an efficient CGJ layer, Embodiment 6 may have very highcurrent efficiency and EQE values of 41.15 cd/A and 16.32%.

Also, it can be seen that Embodiment 6 has the maximum luminance of29,500 cd/m² at the operating voltage of 28 V.

FIG. 14A is an image illustrating emission of a multi-stacked white LEDaccording to an embodiment, and FIG. 14B is a graph showing an emissionspectrum of a multi-stacked white LED according to an embodiment.

Referring to FIGS. 14A and 14B, it can be seen that Embodiment 6(3-stacked white QLED) emits white light, a blue light emitting layerhas a peak at 447 nm, a green light emitting layer has a peak at 522 nm,and a red light emitting layer has a peak at 625 nm.

Also, with respect to Embodiment 6, the blue, green, and red lightemitting layers respectively have the full width at half maximum (FWHM)of 24 nm, 33 nm, and 28 nm.

Also, it can be seen that green light has relatively great EL intensitycompared to that of red light and blue right if the luminance ofEmbodiment 6 is 20 mA/cm².

4. Electrical Properties of OLED

FIGS. 15A and 15B are cross-sectional views illustrating an LED (e.g.,OLED) based on presence or absence of a CGJ layer according to acomparative example and an embodiment, and FIGS. 15C and 15D arecross-sectional views illustrating an inverted LED (e.g., OLED) based ona presence or absence of a CGJ layer according to a comparative exampleand an embodiment.

FIGS. 15A to 15D are cross-sectional views respectively illustratingdetailed structures of Comparative example 1, Embodiment 7, Comparativeexample 2, and Embodiment 8.

Referring to FIGS. 15A to 15D, it can be seen that, in Comparativeexample 1, a hole injection layer 320 including a p-type oxide isprovided, in Embodiment 7, a CGJ layer 420 is formed on an anode 410, inComparative example 2, a hole injection layer 520 including an n-typeoxide is provided, and, in Embodiment 8, a CGJ layer 620 is formed on ananode 610.

In detail, referring to FIG. 15A, an LED 300 of Comparative example 1may include an anode 310, the hole injection layer 320, a hole transportlayer 330, a light emitting layer 340, an electron transport layer 350,and a cathode 360.

Here, the LED 300 of Comparative example 1 may be manufactured by usingITO for the anode 310, Cu₂SnS₃—Ga₂O₃ for the hole injection layer 320,TCTA/NPB for the hole transport layer 330, TCTA:TPBi:Ir (ppy)₃ for thelight emitting layer 340, TPBi for the electron transport layer 350, andLiF/Al for the cathode 360.

Referring to FIG. 15B, an LED 400 of Embodiment 7 may include the anode410, the CGJ layer 420 including an n-type oxide 421 and a p-type oxide422, a hole transport layer 430, a light emitting layer 440, an electrontransport layer 450, and a cathode 460.

Referring to FIG. 15C, an LED 500 of Comparative example 2 may includean anode 510, the hole injection layer 520, a hole transport layer 530,a light emitting layer 540, an electron transport layer 550, an electroninjection layer 560, and a cathode 570.

Referring to FIG. 15D, an LED 600 of Embodiment 8 may include the anode610, the CGJ layer 620 including an n-type oxide 621 and a p-type oxide622, a hole transport layer 630, a light emitting layer 640, an electrontransport layer 650, an electron injection layer 660, and a cathode 670.

Hereinafter, the improvement in the electrical efficiency of an LEDaccording to a CGJ layer formation will be described by comparingelectrical properties between Comparative example 1 and Embodiment 7 andbetween Comparative example 2 and Embodiment 8.

FIG. 16 is a graph showing current efficiency-luminance-power efficiencyproperties of an LED according to a comparative example and anembodiment.

Referring to FIG. 16, it can be seen that current efficiency and powerefficiency values of Embodiment 7 (OLED 2) are greater than those ofComparative example 1 (OLED 1).

Through this, the excellent charge generation and transport capabilityof the CGJ layer formed in Embodiment 7 may be verified.

FIG. 17 is a graph showing current efficiency-luminance-power efficiencyproperties of an inverted LED according to a comparative example and anembodiment.

Referring to FIG. 17, it can be seen that current density, luminance,current efficiency and power efficiency values of Embodiment 8 (OLED 4)are greater than those of Comparative example 2 (OLED 3).

Through this, the excellent charge generation and transport capabilityof the CGJ layer formed in Embodiment 8 may be verified.

Also, a CGJ layer according to embodiments may apply to various types ofLEDs, such as, for example, a QLED and an OLED, and may implement theexcellent charge generation and transport capability.

While this disclosure includes specific embodiments, it will be apparentto those skilled in the art that various alterations and modificationsin form and details may be made in these embodiments without departingfrom the spirit and scope of the claims and their equivalents. Forexample, suitable results may be achieved if the described techniquesare performed in a different order, and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner, and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. A light emitting device (LED) comprising ananode, a hole transport layer, a light emitting layer, and a cathode,the LED comprising: a charge generation junction (CGJ) layer in alayer-by-layer structure in which an n-type oxide and a p-type oxideformed on at least one surface of the light emitting layer aresequentially stacked, wherein the n-type oxide includes zinc oxide(ZnO), and the p-type oxide is represented by the following formula:Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula] where 0.2<x<1.5.
 2. The LED ofclaim 1, wherein the n-type oxide and the p-type oxide have the band gapenergy of 3.0 eV or more.
 3. The LED of claim 1, wherein the n-typeoxide is ZnO doped with a dopant.
 4. The LED of claim 3, wherein thedopant includes at least one of cesium (Cs), lithium (Li), aluminum(Al), magnesium (Mg), indium (In), and gallium (Ga).
 5. The LED of claim1, wherein the light emitting layer includes at least one of a quantumdot, an oxide layer, a nitride layer, a semiconductor layer, an organiccompound layer, an inorganic compound layer, a phosphor layer, and a dyelayer.
 6. The LED of claim 1, wherein the LED has the current efficiency(CE) of 1 cd/A to 100 cd/A.
 7. The LED of claim 1, wherein the LED hasthe external quantum efficiency (EQE) of 5% to 25%.
 8. A multi-stackedlight emitting diode (LED) comprising an anode, a hole transport layer,at least two light emitting layers, and a cathode, the multi-stacked LEDcomprising: a charge generation junction (CGJ) layer in which alayer-by-layer structure in which an n-type oxide and a p-type oxide aresequentially stacked is formed between the at least two light emittinglayers, wherein the n-type oxide includes zinc oxide (ZnO), and thep-type oxide is represented by the following formula:Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula] where 0.2<x<1.5.
 9. Themulti-stacked LED of claim 8, wherein the n-type oxide and the p-typeoxide have the band gap energy of 3.0 eV or more.
 10. The multi-stackedLED of claim 8, wherein the n-type oxide is ZnO doped with a dopant. 11.The multi-stacked LED of claim 10, wherein the dopant includes at leastone of cesium (Cs), lithium (Li), aluminum (Al), magnesium (Mg), indium(In), and gallium (Ga).
 12. The multi-stacked LED of claim 8, whereinthe multi-stacked LED has the current efficiency (CE) of 3 cd/A to 300cd/A.
 13. The multi-stacked LED of claim 8, wherein the multi-stackedLED has the external quantum efficiency (EQE) of 15% to 75%.
 14. Amethod of manufacturing a light emitting device (LED), the methodcomprising: forming an anode on a substrate; forming a hole transportlayer on the anode; forming a light emitting layer on the hole transportlayer; forming a cathode on the light emitting layer; and forming acharge generation junction (CGJ) layer on at least one surface of thelight emitting layer, wherein the CGJ layer is formed through filmformation with a solution that includes an n-type oxide including zincoxide (ZnO) and a p-type oxide represented by the following formula:Cu₂Sn_(2-X)S₃—(Ga_(X))₂O₃  [Formula] where 0.2<x<1.5.
 15. The method ofclaim 14, wherein the CGJ layer is applied with heat treatment orultraviolet (UV)/ozone treatment.
 16. The method of claim 15, whereinthe heat treatment is performed at 150° C. to 250° C.
 17. The method ofclaim 15, wherein the heat treatment is performed for 10 minutes to 90minutes.
 18. The method of claim 15, wherein the UV/ozone treatment isperformed for 30 seconds to 5 minutes.